It is well known that measurements of blood glucose can be made by placing a drop of blood on a prepared reagent pad, allowing the blood to react with the materials on the pad for a fixed period of time, washing and then removing excess water from the pad, and then evaluating the color of the reacted area by comparison with a standard. The enzyme glucose oxidase catalyzes the oxidation of glucose in blood by oxygen in the atmosphere, producing gluconic acid and hydrogen peroxide. In the presence of peroxidase, chromogens in the reduced form are oxidized by the hydrogen peroxide and produce colors which range from gray to blue-purple. To avoid the inherent problems associated with visual comparison with a chart, a reflectometer using a light source, a photocell and electronic color evaluation is usable. One device suitable for this purpose is the blood glucose meter marketed by the Ames Division, Miles Laboratories, Inc., Elkhart, Ind.
While the theory is sound and while tests of this type can be performed to give accurate results, there are some serious practical problems in that the various steps must be performed with considerable precision in order for the results to be reliable. Specifically, the reaction time, i.e., the duration of the interval during which the blood is allowed to react with the materials in the pad, is quite critical.
Also, in order for the test results to be comparable, the washing must be performed in the same way each time and, after washing, the removal of excess water, often accomplished by blotting, must be done in a consistent fashion. If these steps are not done the same way each time, the blood samples from a single patient can be evaluated to indicate either a significant change in glucose level when none has actually occurred, or the reverse. While the experienced, skilled laboratory technician can obtain good results consistently, an inexperienced one may not. Of even more importance, a person attempting to perform the test at home may obtain widely varying measurements, resulting in over- or under-medication. It is important for some patients, particularly diabetics, to be able to conduct such tests on their own and the glucose meter mentioned above is sold for that purpose. However, unless the instructions are followed with precise consistency, it has been found that 30% or more of the measurements can be in error.